1. Field of the Invention
The present invention relates generally to a testing apparatus for a power transmission of an automotive vehicle, which performs endurance testing, gear shifting transition characteristics testing and so forth. More specifically, the invention relates to a power source unit employing a motor, such as electric motor, hydraulic motor and so forth, as a prime mover and having equivalent acceleration and deceleration characteristics to an automotive internal combustion engine.
2. Description of the Background Art
In the prior art, most transmission testing apparatus employs an automotive internal combustion engine, for which a power transmission to be tested is to be coupled, as a driving power source. The transmission test apparatus performs endurance testing and gear shifting transition testing and so forth. Such conventional testing apparatus have had various problems.
For instance, in order to use the internal combustion engine, various engine accessories, such as a fuel supply system, exhaust system, ignition system and so forth, are required. Furthermore, in order to maintain the clean testing environment, a ventilation system, noise-proof facility and so forth are required. In addition, since the fuel used for the driving engine has high flashing ability, high attention has to be paid to flashing. Because of various requirements for the facility, cost for the facility and administration become substantially high. Furthermore, setting up the facility requires substantial working times.
The internal combustion engine tends to be influenced by environmental conditions, such as atmospheric temperature, atmospheric pressure and so forth, which varies engine output. Therefore, the result of a test can be fluctuated by the engine condition and environmental condition. Therefore, reliability of the test result is at a low level.
Also, since the test is performed by utilizing the engine to be actually used with the transmission, the transmission test cannot be performed unless the actually used engine is provided. Namely, when a new engine and transmission are to be developed, testing of the transmission cannot be performed until the engine designing is completed. Therefore, development of the transmission is always delayed in relation to timing of completion of the engine designing.
In order to solve the foregoing problems, Japanese Patent First (unexamined) Publications (Tokkai) Showa 58-38833 and 61-53541 propose motor powered transmission testing apparatus which employs an electric motor, a hydrostatic motor as driving power source. Such prior proposed motor powered transmission testing apparatus is effective for performing endurance tests and steady state characteristics tests. However, because of much greater inertia moment in the motor, a difficulty is encountered in shifting transition characteristics tests which is important for analysis of shifting shock and enhancing transmission shifting characteristics.
Namely, in case of the electric motor, the inertia moment becomes in excess of ten times of that of the internal combustion engine, as set out in Tokkai Showa 61-53541 set forth above. For avoiding the influence of the substantially large inertia moment of the electric motor, a command value of a current command for the electric motor is corrected for compensating the difference of inertia moment and adapting transition characteristics of driving torque when the set torque varies.
In this case, though the driving torque transition characteristics can be adjusted to be equivalent to that of the actual engine, the revolution speed of the motor fluctuates due to variation of the current command value to make it difficult to obtain transmission shifting transition characteristics data equivalent to that obtained utilizing the actual engine.
On the other hand, in case of the hydrostatic motor which is normally used in combination with a speed increasing device, this generally increases the motor revolution speed twice or three times. By utilizing the speed increasing device, the inertia moment in the driving power source can be reduced. However, the prior proposed hydrostatic motor powered transmission test apparatus is still unsatisfactory in avoiding influence of the inertia moment.
A step-up gear unit is adapted for realization of an automotive internal combustion engine simulated driving power supply in use with motor such as an electric motor, a hydraulic motor and so forth. The step-up gear unit is connected to at least two motors for selectively outputting driving torque of sole motor and combined torque of both motors for wider capacity range of capacity of engine to simulate. The gear train of the step-up gear is so composed to selectively connect and disconnect the motors to an output gear for selective output of the driving torque.
As will be appreciated from the discussion given hereabove, the following power output characteristics may be required for a power source unit to be used as replacement of the internal combustion engine.
First of all, the inertia moment in revolution may have substantial influence for mode of shift shock to be caused in the power transmission. Therefore, unless the inertia characteristics of the power source, such as the motor, is equivalent to that of the engine, the inertia moment on the motor has to be significantly reduced.
Secondly, because the motor has substantial mechanical delay in responding to variation of the electric command, one must obtain response characteristics equivalent to that of the engine in relation to the throttle valve angular displacement. Particularly, upon starting of vehicular traveling, the throttle angular displacement becomes substantial. In general, the motor cannot follow such abrupt variation of the commanding value. Therefore, the response characteristics of the motor upon vehicular starting-up becomes far different from that of the engine. Therefore, unless the power output characteristics is adapted to be equivalent to that of the engine, shifting transition characteristics of the transmission cannot be obtained as a reliable data.